Network Drive mapping not appearing in My Computer or Explorer

I have a strange problem with Network drive mappings not appearing in My
Computer and Explorer. The strange thing is that the network drive mappings
do appear in application like office. This happens at random times and is
fixed by getting the user to log out and back in again. The Network drives
are mapped by a login script that does an LDAP query of the AD and then maps
the network drives according to group membership. The network is made up of
Windows 2003 domain controllers and Windows XP SP1 Workstations.